Muscle Injury and Repair


Muscle injuries account for ~46% of American football injuries. 92% affect the four major muscle groups of the lower limbs: hamstrings 37%, adductors 23%, quadriceps 19% and lower leg 13%. As much as 96% of all muscle injuries in football/soccer occur in non-contact situations. Approximately 16% of all muscle injuries in football/soccer are re-injuries and associated with 30% longer absence from competition than the original injury.

From 2004-2007 of 34,006 medical evacuations from Iraq and Afghanistan, the most common were non-combat musculoskeletal injuries (24%). Such injuries may include muscle strains, contusions, tendinopathy, fasciitis, bursitis, muscle/tendon tears and ruptures, joint sprains and dislocations, and fractures.

Skeletal Muscle is the most abundant tissue in the body; it is essential for breathing, posture, and motion. It serves important roles in homeostasis and metabolism; e.g. heat production and carbohydrate or amino acid (protein) storage. Loss of muscle function in acute or chronic conditions can result in decreased mobility and strength as well as metabolic dysfunction. When tissues are injured during infection or after mechanical injury, the inflammatory process is triggered in response to damage-associated molecular patterns released by dead and dying cells. These cell mediators (chiefly Macrophage variants) are released in the local tissue microenvironment where they regulate inflammation, tissue repair, regeneration, and resolution. The duration and intensity of the various inflammatory components must be coordinated with the degree of muscle damage and the need to change cellular milieu during repair.

Abnormal muscle repair can occur in the context of fiber degeneration eventually leading to the substitution of normal muscle architecture by fibrotic (scar) tissue. When the healing sequence is organized and controlled the inflammatory response resolves quickly and normal architecture is restored. The composition of the inflammatory cells is dynamically regulated to facilitate timely initiation of their divergent functions. How-ever if the healing response is chronic (>3 months) or dysregulated it can lead to pathological fibrosis (scarring) impairing normal tissue elasticity and contractility. This ab-normal repair results in decrease functional strength and motion and ultimately pain. Interfering with the inflammatory response immediately after acute injury by repetitive irritating activity in sport, training, or operational environments disrupts the removal of neurotic fibers and impedes seeding of new muscle fibers.

It is important to note that the exact mechanisms of tissue repair and return to homeo-stasis are still under debate and not fully understood. However current information tells us that the process of injury to repair is a complex synchronized molecular (cellular) process. We commonly think of inflammation as a “bad thing” that results in swelling, redness, pain, and decreased function. There are times when we want allow inflammation to take its course and, in some cases, even stimulate. There times when we may impede the healing process by taking NSAIDs, using ice or heat, or continued repetitive activity.



Muscle Injury Grades

Grade I: No tear, loss of strength, or loss of function. Mild inflammatory response

Grade II: Mild to moderate tissue damage with reduced strength and function

Grade III: Complete tear and loss of function





Risk Factors for Musculoskeletal Injuries

  • Poor Nutrition

  • High Running Mileage

  • Low Aerobic fitness & Endurance

  • Prior injury

  • Recreational Sports

  • Limited hx of prior activity

  • Age of running shoes

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Acute vs. Chronic injury

As described in last month’s newsletter, acute tissue injury involves an orchestrated influx of inflammatory cells and resident stem cells in a series of events to restore tissue homeostasis. However

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